Colorimetry or Colourimetry can refer to:
Colorimetric equipment is similar to that used in spectrophotometry. Some related equipment is also mentioned for completeness.
In physical chemistry
, a colorimeter
is a device used to test the concentration of a solution by measuring its absorbance of a specific wavelength of light. To use this device, different solutions
must be made, and a control (usually a mixture of distilled water
and another solution) is first filled into a cuvette
and placed inside a colorimeter to calibrate the machine. Only after the device has been calibrated can you use it to find the densities and/or concentrations of the other solutions. You do this by repeating the calibration, except with cuvettes filled with the other solutions.
The filter on a colorimeter must be set to red if the liquid is blue. The size of the filter initially chosen for the colorimeter is extremely important, as the wavelength of light that is transmitted by the colorimeter has to be same as that absorbed by the substance.
In digital imaging
, colorimeters are tristimulus devices used for color calibration
. Accurate color profiles
ensure consistency throughout the imaging workflow, from acquisition to output.
Spectroradiometer, Spectrophotometer, Spectrocolorimeter
The absolute spectral power distribution
of a light source can be measured with a spectroradiometer
, which works by optically collecting the light, then passing it through a monochromator
before reading it in narrow bands of wavelength.
Reflected color can be measured using a spectrophotometer (also called spectroreflectometer or reflectometer), which takes measurements in the visible region (and a little beyond) of a given color sample. If the custom of taking readings at 10 nanometer increments is followed, the visible light range of 400-700nm will yield 31 readings. These readings are typically used to draw the sample's spectral reflectance curve (how much it reflects, as a function of wavelength); the most accurate data that can be provided regarding its characteristics.
The readings by themselves are typically not as useful as their tristimulus values, which can be converted into chromaticity co-ordinates and manipulated through color space transformations. For this purpose, a spectrocolorimeter may be used. A spectrocolorimeter is simply a spectrophotometer that can estimate tristimulus values by numerical integration (of the color matching functions' inner product with the illuminant's spectral power distribution). One benefit of spectrocolorimeters over tristimulus colorimeters is that they do not have optical filters, which are subject to manufacturing variance, and have a fixed spectral transmittance curve—until they age. On the other hand, tristimulus colorimeters are purpose-built, cheaper, and easier to use.
The CIE recommends using measurement intervals under 5nm, even for smooth spectra. Sparser measurements fail to accurately characterize spiky emission spectra, such as that of the red phosphor of a CRT display, depicted aside.
Color temperature meter
use information provided by these meters to decide what color correction
should be done to make different light sources appear to have the same color temperature. If the user enters the reference color temperature, the meter can calculate the mired
difference between the measurement and the reference, enabling the user to choose a corrective color gel
or photographic filter
with the closest mired factor.
Internally the meter is typically a silicon photodiode tristimulus colorimeter. The correlated color temperature can be calculated from the tristimulus values by first calculating the chromaticity co-ordinates in the CIE 1960 color space, then finding the closest point on the Planckian locus.